Bridge components or bridges are components that are used to interconnect Local Area Networks (LANs). A bridge interconnects the LANs in such a way that one workstation within a first LAN can be reached by other stations connected in other LANs as though they were all connected to the same LAN. For example, FIG. 1 shows an existing bridged LAN network (BLN) 100. The BLN is made up of a plurality of LANs 102A-D. In this particular example, four LANs are shown labeled A, B, C and D. Each of the LANs contains at least one workstation 104. Each workstation 104 is connected to every other workstation and to a bridge component 106A-D to allow communication within that particular LAN. Additionally, links 108 exist between each bridge 106 of each LAN 102 to enable data to be transferred between LANs in a substantially seamless manner.
As data moves through the network, there may be multiple paths the data may take to arrive at the same destination. To avoid the problem of loops being created in the network, various protocols have been devised to create a loop-free topology. In one existing example, bridges 106 execute a Spanning Tree Protocol (STP) which is explained in detail in IEEE 802.1D, herein incorporated in its entirety by reference. The STP determines for each port of a bridge whether such port should be placed in a blocking mode, where no traffic is accepted or sent by the port, or placed in a forwarding mode, where traffic may be sent and received by said port. By strategically blocking ports to certain links in accordance with the STP, loops are eliminated and the network runs in an efficient and loop free manner.
It is understood that in a sophisticated interconnection of various workstations 104 and LANs 102 to create the BLN 100, it is sometimes required to update the software on a bridge 106 to provide the best possible operating conditions within the BLN 100. Currently, updating of a bridge 106 requires all ports of the bridge (e.g., ports P1-P4 of bridge 106D) be put into a blocking state. By placing all ports P1-P4 in the blocking state, normal network traffic is not allowed to flow through the bridge thereby creating a temporary bottleneck in this portion of the BLN 100. Once all ports P1-P4 are placed in the blocking state, new software is installed into the bridge 106.
After the updating is completed, it is necessary to restart the protocol (e.g., the STP) to reestablish the loop free topology that existed prior to the bridge being taken “offline” (i.e., the ports being blocked). This procedure leads to two possible reconfigurations of the spanning tree. The first reconfiguration may occur before the restart, when the bridge blocks all its ports. This blocking of ports may lead to permanent loss of connectivity. The second reconfiguration may occur after the restart is completed, and the original connectivity is restored. Each reconfiguration influences the traffic in the network. Due to the reconfiguration, traffic may flood (i.e., be routed to all possible paths at all available bridges) which leads to an increased network load. Additionally, connectivity may be lost between users of the BLN 100 for a period of up to 50s (depending on the particular spanning tree protocol and the particular circumstances). As such, it is desirable to have a means and method for updating network bridges and subsequently re-establishing the original loop-free topology without causing reconfiguration of same or creating network congestion.